Shay Lally Quantity surveyor

.IN OUR BRAND-NEW series, The Big Reno Clinic, Houses to Restore QS Shay Lally provides answers and solutions to the big (and little, but important) questions you may have about making the most of your home.

Send your question to reno@thejournal.ie 

This week’s question:

I have an old extension that I think needs to be rebuilt. What would it cost to rebuild an old extension that’s about 20 square metres?

Shay says:

Many older houses have extensions that were poorly built at the time of construction and are now in a poor state of repair. The first thing I’d suggest doing before committing to redoing the extension is to assess its condition. Sometimes older extensions are structurally sound and just require a new roof, some insulation and modernising. Opting to do this can result in big savings.

That said, many older extensions need so much work done to them it would make more sense to demolish them and rebuilding it.

To redo an old extension the following costs need to be considered:

Demolition and removal of the existing extension

This might sound like stating the obvious but if the existing extension needs to go, there are other things that need to be done before demolition and the cost factored in. This can include some temporary works as well as prep to plumbing, heating and electrical works.

Prior to demolishing the extension you’d need a plumber on site to isolate out the heating and plumbing. If you have a gas boiler in the extension you’ll need a registered gas installer to blank off the gas and remove the boiler prior to any works commencing. Similarly you’ll need an electrician to disconnect the circuits relating to the light and electrical points in the house.

Lastly you’ll need to consider any temporary works – temporary works are required to keep the existing house secure and protected after the extension is demolished and the new extension is being built.

The new extension

The next cost to consider is that of the new extension itself. Depending on the design and building materials you choose, the cost per square metre could range from €3,500 – €5,500 per square metre.

I covered the impact building materials and internal finishes have on build costs in my column last week. An extension finished in a sand and cement render, with a torch-on roof covering and uPVC windows will cost less to build than an extension with a brickwork finish, aluclad windows and a zinc roof covering.

Similarly, fitting laminate floors, installing standard white electrical sockets and switches along with applying standard paint will result in a lower cost per square metre than fitting a timber engineered floor, using a premium paint brand and fitting high quality sockets and switches.

Structural alterations: connecting an extension to a house

Another thing that’s often overlooked when discussing the cost of extending is the cost of any structural openings required to connect the house with the new extension. Typically this involves removing or partially removing the back wall of the house.

In this reader’s case, given there’s an existing extension in place, I appreciate that the existing openings may already be formed and no additional structural alterations may be required. That said, many older extensions are badly connected with the original house and feel like something that’s stuck on as opposed to something that’s been well considered.

Redoing an extension provides an opportunity to ensure your house and your extension adequately flow – this is where good design comes in.

To connect a house and an extension requires making structural alterations to the back walls of the house that involves installing some temporary supports before cutting and removing a section of the back wall and installing the necessary steel beams and columns.

If you’re demolishing the complete back of the house you will likely need what’s referred to as a goal post. This means you’ll have a vertical column at either end of the wall and the supporting steel beam is placed, bolted and welded in place. There’s the added cost of making good to the rooms affected by these alterations at the back wall of the house. You’ll likely end of replacing some of the other finishes in those rooms too.

Professional fees

The cost of professional fees are often overlooked when budgeting. In reality there’s the build cost plus professional fees plus other expenses like storage, temporary accommodation, furniture or client supply fixtures and fittings like light fittings for example. I will go into more detail on the anticipated cost of professional fees below.

Total cost

Based on a 20m2 extension the cost range I would advise would be as follows:

Demolitions, waste removal of existing extension and allowance to cover the plumber and electrician plus the cost of any important works €10,000 – €15,000 inclusive of VAT

Cost to build a new extension €3,500 – €5,500 per metre squared inclusive of VAT. Based on 20m2 the cost for this would be between €70,000 and €110,000 inclusive of VAT.

Cost for demolishing some or all of the back wall of your house €5,000 – €15,000*

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*please note these costs would covered an opening of between 3m and 8m any bigger or more complex would need to be assessed separately.

The cost of professional fees includes an architect, a quantity surveyor and a structural engineer:

An architect would be between €5,000 and 12% of the total build cost.

A structural engineer would between €3,500 and €5,500 depending on the complexity of the design.

A quantity surveyor would cost between €5,000 and €10,000. €5,000 would cover the production of a bill of quantities, completing a tender analysis and appointing a contractor. €10,000 would be for the above along with provided a cost management service throughout the entire project based on a four- to five-month build.

On a project like this professional fees may cost between €13,500 and €28,700 depending on the level of services the consultants provide and the complexity of the design.

In total the cost to redo your 20m2 extension will cost between €98,500 and €153,700.

Broken down that works out as €4,925 and €7,685 per m2 inclusive of VAT.

Key takeaways

• Before committing to redoing an extension assess the condition of the existing extension and establish if it’s possible to refurbish what’s already there. Opt for the most cost-effective option provided it meets your needs.
• Remember that the building materials and finishes you choose have an impact on the cost per m2.
• It’s wise to ensure the existing house and the extension flow. Any structural work required to this will come at a cost and isn’t included in the cost per m2.
• When assessing your budget it’s important to consider and include professional fees.
• There are additional costs too that need to be considered on a case by case basis. These include storage, temporary accommodation, new furniture or client supply fixtures and fittings.

Shay will be back answering your questions next week.

Send him your queries on managing a renovation in the comments or to reno@thejournal.ie